The present invention relates to packing devices and, more particularly, to seals, packings and the like used in environments wherein at least a portion of the sealing device is subjected to extrusion forces.
Sealing devices, such as seals or packings, whether of the dynamic or static type, are usually made, or have portions made of materials which, to some extent, are resilient or at least deformable. In order to seal effectively, it is necessary that the sealing device be placed under some compressive loading between the components of the assembly to be sealed. Because of the compressing load and the deformable nature of at least a portion of the seal, and if the seal is subjected to sufficient pressure, there is a tendency for portions of the seal to be subjected to extrusion forces which will either distort the seal and impair its effectiveness as a seal or, in more severe cases, force portions of the seal into clearances between the components to be sealed.
In an attempt to overcome this extrusion problem, workers in the field have resorted to various techniques. One common practice employed to prevent such extrusion as, for example, in a seal ring or packing used between relatively reciprocating or rotating parts, is to mount separate back-up rings or washers adjacent the seal ring, the back-up ring serving to prevent the seal ring from being extruded. These back-up rings are generally made of metal or other hard materials which generally must be machined. Another technique which has been used is shown in U.S. Pat. No. 3,094,337 wherein there are disclosed anti-extrusion seal rings in which an annulus of a relatively soft sealing material is bonded to annular sections of anti-extrusion materials such as thermosetting resins or the like.
U.S. Pat. No. 4,219,204 shows anti-extrusion sealing devices having annular sections reinforced with a knitted material formed from interlocking filaments.
Another patent U.S. Pat. No. 3,719,366 shows an anti-extrusion packing having a reinforcing material comprised of a strip of fabric wound into a helix, with convoluting of the helix wound upon one another and bonded into integral sections.
Frisby et al. U.S. Pat. No. 2,446,224 shows an oil sealing ring having rings coiled upon one another with an offset that permits their contraction.
In some applications for packing devices it is necessary for the anti-extrusion element to elongate or stretch, or be twisted or otherwise altered in configuration. Although the standard oil spring or garter spring has been used as an anti-extrusion device in seals, it is found that the packing material has a tendency to extrude between adjacent coils of the spring when the packing is subjected to extreme pressures. Also, the garter spring, being made from a round wire, tends to leave impressions on metal surfaces that it contacts under pressure and may cause eventual seal failure.
It is therefore an object of the present invention to provide a new and improved anti-extrusion packing device that prevents extrusion of the packing material in its intended use and also which may be elongated or deformed without causing failure of the device or wear of sealed parts.